The present invention relates generally to automotive differentials and, more particularly, to a differential case having an optimized geometry for the assembly windows formed therein.
Differentials are used in the drivetrain of motor vehicles for delivering drive torque to the wheels while permitting speed differentiation therebetween. Referring to FIGS. 1 and 2, a prior art differential 10 is shown to include a differential case 12 supported at its opposite axial ends by bearing assemblies 14 for rotation relative to a differential carrier or housing 16. Housing 16 can be part of an axle assembly of the type used in rear-wheel drive vehicles or, in the alternative, can be incorporated into the transaxle of a front-wheel drive vehicle. Differential case 12 is formed to include an enlarged interior chamber 18 within which a gearset is retained. Differential case 12 also includes a pair of first apertures 20 and a pair of second apertures 22, with both pairs of apertures communicating with chamber 18. In addition, differential case 12 includes a radial flange 24 to which a ring gear 26 is secured, such as by bolts 28. A pinion shaft 30 extends between first apertures 20 and is rigidly fixed to differential case 12 by a locking pin 32 retained in a bore 33.
The gearset includes a pair of pinion gears 34 which are supported on pinion shaft 30 within chamber 18 for rotation about its longitudinal axis, denoted in FIG. 1 by construction line "A". Each pinion gear 34 is meshed with a pair of side gears 36 which, in turn, are each journally supported for rotation about the longitudinal axis of differential case 12, denoted by construction line "B". The axial ends of differential case 12 define a pair of tubular hubs 38 and 40 which journally support a pair of axle shafts 42 and 44, respectively, and upon which bearing assemblies 14 are mounted. One end of axle shaft 42 is fixed (i.e., splined) to one of side gears 36 while its opposite end is fixed to one of the vehicle's wheels. Similarly, one end of axle shaft 44 is fixed (i.e., splined) to the other one of side gears 36 while its opposite end is fixed to the other of the vehicle's wheels. As is conventional, ring gear 26, and differential case 12 to which it is attached, are rotated within housing 16 by an input drive pinion (not shown) which is secured to the end of a drive shaft (not shown). As such, rotary motion of case 12 is delivered to axle shafts 42 and 44 through engagement of pinion gears 34 and side gears 36 to permit relative rotation therebetween.
According to the conventional assembly process for differential 10, side gears 36 and then pinion gears 34 are sequentially assembled into chamber 18 by passing them through second apertures 22, hereinafter referred to as assembly windows. Referring to FIG. 2, one of assembly windows 22 is shown to be generally elliptical in shape with an axial dimension "X" and a circumferential or lateral dimension "Y". A significant design constraint is that lateral dimension "Y" has traditionally been greater in size than the outer diameter of side gears 36 so as to allow entry thereof into chamber 18 and to permit subsequent alignment of side gears 36 relative to rotary axis "B". Similarly, axial dimension "X" must be greater in size than the outer diameter of pinion gears 34 to permit entry thereof into chamber 18 and subsequent alignment in meshed engagement with side gears 36. Thereafter, pinion gears 34 are rotated into alignment with first apertures 20 for receipt of pinion shaft 30. Due to this window geometry, design compromises are required since barrel segment 48 of differential case 12 must be thick enough to withstand the maximum bending stresses that are anticipated to be applied thereon during the service life of differential unit 10 while still maintaining the smallest outer diameter (i.e., ring gear pilot diameter) as possible. Moreover, the material of choice has previously been limited to ferrous materials such as, for example, cast iron to accommodate these bending stresses.